Recovery of molybdenite

ABSTRACT

Low-grade molybdenite flotation products are leached with water at elevated temperature and pressure in an oxidizing atmosphere to selectively dissolve copper, with some sulfur and iron, from sulfide minerals normally present so as to increase the recovery of molybdenite in marketable concentrates.

United States Patent 1191 Bloom et a1.

[ 1 Jan. 30, 1973 [54] RECOVERY OF MOLYBDENITE [75] Inventors: Philip A, Bloom, Stufrt J both of Salt Lake City, Utah; Lamar Evans, Salt Lake City, Utah [73] Assignee: The United States of America as represented by the Secretary of the Interior [22] Filed: Nov. 17, 1970 [21] Appl. No.: 90,096

52 us. Cl. ..423/53, 75/2, 75/117,

[51] Int. Cl ..C22b 3/00, 303d 1/00, C22b 15/00 [58] Field ofSearch ..75/1,2,l01, 113,117,121, 75/97, 114

[56] References Cited UNITED STATES PATENTS 3,117,860 l/1964 Bjerkerud ..75/1

3,544,309 12/1970 Fletcher 3,544,306 12/1970 McGauley.....

3,455,677 7/1969 Litz 3,196,107 7/1965 Tomic ..75/117 3,429,693 2/1969 Bauer ..75/101 R 2,746,859 5/1956 McGauley.. ..75/117 3,053,614 9/1962 Foos ..75/101 1,681,528 8/1928 Elliott ..75/117 2,822,261 2/1958 Mackiw ..75/117 2,796,344 6/1957 Brennan ..75/121 3,196,004 7/1965 Kunda ..75/121 3,458,277 7/1969 2,965,447 12/1960 Zimmerley ..75/101 R FOREIGN PATENTS OR APPLICATIONS 635,269 1962 Canada ..75/1

Primary Examiner-Winston A. Douglas Assistant Examiner-Peter D. Rosenberg Att0rney-Ernest S. Cohen and William S. Brown [57] ABSTRACT with some sulfur and iron, from sulfide minerals normally present so as to increase the recovery of molybdenite in marketable concentrates.

3 Claims, No Drawings RECOVERY OF MOLYBDENITE EXAMPLE 1 A considerable portion of the world production of molybdenite is obtained as a by-product from the concentration of copper sulfide from molybdenite-bearing porphyry deposits. Common practice at copper concentrators is to float a bulk copper sulfide-molybdenite concentrate containing approximately 1 percent M082. The molybdenite is then separated by flotation in a rougher concentrate which is upgraded by flotation or a combination of flotation and heating to a product 1 usually containing 85 to 90 percent M08, and a maximum of 1 percent copper. The small amount of copper left is sometimes then removed chemically with cyanide.

It has now been found, in accordance with the present invention, that the recovery of molybdenite, as a marketable concentrate, from low-grade molybdenite flotation products can be increased by leaching with water, at elevated temperature and pressure in an oxidizing atmosphere, to selectively dissolve copper, with some sulfur and iron, from sulfide minerals normally present. The process of the invention has been found to be effective to raise the grade of low-grade flotation leachmg i the content of the bomb was lemoved products from Starting materials containingv about 75 and the residue was separated from the leach liquor by percent MoS to finished products containing about 80 mtranon' to 90 percent MOS2 After sub ecting 50 grams of the concentrate 11'] 450 Starting materials for the process of the invention are mllhmel's of water to 245 P Oxygen p f at a F typically molybdenite flotation products containing, in permuted C 3ofmmute P 3 resldue weight percent, about 45 Mo 5 M032), about 3 Cu was obtained that contained, in percent, 51.7 Mo (86.2 (largely in the form of sulfides), and about6 Fe (in the 2) and Fe, and accounted for a A sample of molybdenite concentrate was obtained from a copper concentrator in the Tucson, Ariz. area. A partial analysis revealed it to contain, in percent, 45.2 Mo (75.4 M'oS 2.84 Cu, 6.1 Fe, and 6.0 insolubles. The major minerals present were molybdenite, chalcocite, chalcopyrite, pyrite, and quartz. The sample, as received from the mill, was filtered, dried, and stored for use as needed.

Equipment used was a high-pressure stainless steel bomb equipped with gauges, fittings, and other parts needed to agitate the slurry and maintain the necessary temperature and pressure.

The test procedure was to place a sample of the bulk concentrate in the pressure bomb together with the appropriate amount of water. The bomb was then sealed and flushed with oxygen. Heat was applied until the slurry was brought to the desired temperature after 20 which oxygen was introduced into the bomb until the necessary pressure was reached. The slurry was then agitated for the required time. Upon completion of the f f lfid recovery of, in percent, 95.3 M0, 1.4 Cu, and 39.1 Fe.

Leaching is accomplished by maintaining an aqueous slurry of the molybdenite concentrate at a temperature EXAMPLE 2 of about 100 to 150 C and an oxygen pressure of Starting with the concentrate of Example 1 and using about 200 to 600 psi for a period of about 30 to 60 the same procedure but varying the conditions by minutes. Concentration of the concentrate in the slurry reducing the temperature to 130 C, increasing the oxwill usually be from about 5 to 15 weight percent. Any ygen pressure to 490 psi and increasing the leach time apparatus, -ga stainless Steel reactor, p l of to 60 minutes, a leach residue was obtained that conproviding the required temperature and pressure, as mi d, i t, 5L6 M (361 M 5 0,25 C d as agitation of the ay be used in the 3.3 Fe with recoveries of, in percent, 97.5 Mo, 6.9.Cu, leaching operation. and 45.0 Fe.

The leaching is preferably carried out in an atmosphere consisting essentially of oxygen; however, a W Ex/KWLET small amounts, e.g., l to 15 psi, ofair or inert gases may A W be present without detrimental effects. The oxygen at- Starting with the concentrate of Example 1 and mosphere is achieved simply by flushing the reaction the Same lJToCedure but varying the conditions to 650 vessel with oxygen prior to pressurizing. psi oxygen pressure, a temperature of 100 C and a Following leaching, the aqueous slurry is removed leach time Of minutes, 3. leach residue was obtained from the reaction vessel and filtered, or otherwise that contained, in percent, 47.9 Mo (79.9 M08 0.60 treated, to separate the residue from the leach liquor. 50 Cu, and 6.0 Fe with recoveries of, in percent, 99.8 M0, The residue is a molybdenite concentrate that will or- 19.0 Cu, and 90.6 Fe. dinarily contain about to percent M08 and only The results of the three examples are summarized in about 0.05 to 1 weight percent of copper. The leached table 1.

TABLE 1.--SUMMARY OF RESULTS OF THE EXAMPLES 1 Original head analyses, in percent, 75.4 MoSz, 2.84 Cu, 6.1 Fe.

'copperfiri solution as sulfatefcan Be recfilered'in'ani 65 Laboratory tests show that about C is a criticzi one of several ways, e.g., by cementation on iron, elecmaximum temperature because molybdenite is leached trolysis or solvent extraction. The invention will be with extreme rapidity above this temperature. Starting more specifically illustrated by the following examples. with the same concentrate as in previous examples and 3 using the same procedure with a temperature of 200 C, an oxygen pressure of 390 psi, and a leach time of 30 minutes, only 82 percent of the molybdenum was recovered in the residue.

The effect of increasing reaction time was shown by tests made, as previously described, upon the same concentrate. The leach conditions and results were as shown in table 2. m

TABLE 2. REAo'rroN TrMiffiK'Tl Leeched concentrate Analysis, percent Recovery, percent Reaction time, hours Mo Cu Fe Mo Cu Fe 1 Tests made at 160 C. and 246 p.s.l. oxygen pressure.

The results in table 2 show tliat by EEFeTin the reaction time, an undesirably large quantity of molybdenum was dissolved.

in the process of the invention, therefore, leach time is an important factor because a long leach time (more than 2 hours) results in undesirable dissolution of molybdenite. in addition, long leach times require more expensive equipment. To achieve a suitably short leach time, the maximum extraction of copper, iron and sulfur, and the minimum dissolution of molybdenite, the leach conditions must comprise temperatures from about to C and oxygen pressures from about 200 to 600 psi.

What is claimed is:

l. A method for increasing the recovery of molybdenite from low-grade molybdenite flotation products 

1. A method for increasing the recovery of molybdenite from low-grade molybdenite flotation products comprising water leaching of the low-grade products in an oxygen atmosphere at temperatures of about 100 to 150* C and pressure of about 200 to 600 psi to selectively dissolve copper in preference to molybdenum.
 2. The method of claim 1, in which the low-grade molybdenite flotation product contains about 75 percent of MoS2 and about 3 percent of Cu. 